1. Technical Field of Invention
Aspects of the invention relate to a projector for projecting an image by use of a liquid-crystal light valve and other light modulating devices.
2. Description of Related Art
Some related art projectors form a color image by combining, through a special prism, images of respective colors separately formed by sending three colors, RGB, of illumination light to three liquid-crystal light valves, for example. See, for example, JP-A-2002-365720. The contrast ratio achievable on such related art projector, at present, has the upper limit of approximately 1000:1.
Meanwhile, on the CRT or a film, a contrast ratio of 3000:1 or higher is obtained, depending on the viewing environment. Incidentally, according to movie directors and movie critics, where contrast ratio is concerned the ultimate target images desired for movies, require a 5000:1 ratio. Taking account of film overshoot (peaks), nearly 6000:1 is considered required in the future.
In the related art projector as above, the black portion brightness can be reduced by regulating the voltage applied to the lamp which is the light source. However, usually, the amount of light can be reduced only to 80% of maximum because of lamp characteristics.
Meanwhile, there is a proposal that an illumination light amount adjusting device be arranged between the light source and the liquid-crystal light valve, as another method to improve the dynamic range of projection images. See, for example, JP-A-2001-100699. Here, the illumination light amount adjusting device can have a polarization plate for achieving a desired illumination light amount by rotation to a certain direction and a ultrasonic motor for regulating the rotation.